In the present energy-saving era, a lot of efforts have been made to develop low-pressure mercury lamps. In particular, fluorescent lamps, specifically compact self-ballasted fluorescent lamps that exhibit high luminous efficiency and long life, are calling attentions as light sources alternative to incandescent lamps. As one example, compact self-ballasted fluorescent lamps may include double-spiral arc tubes formed so that end portions stand vertically and remaining portions are wound in a double spiral around the axis of spiral.
Compact self-ballasted fluorescent lamps including such double-spiral arc tubes have a higher total height than that of incandescent lamps. The problem therefore is that such a compact self-ballasted fluorescent lamp may partially protrude from an existing lighting fixture designed for an incandescent lamp. To solve this problem, the inventors of the present application have come up with the idea that the total height of compact self-ballasted fluorescent lamps can be reduced by winding also the end portions of the arc tube, which had conventionally been formed to stand vertically, into a double spiral around the axis of spiral. With this idea, the inventors have succeeded in downsizing compact self-ballasted fluorescent lamps to substantially the same size as incandescent lamps.
FIG. 1 shows a holding member for holding an arc tube whose end portions are formed in a double spiral. As shown in the figure, the holding member 906 is in a cylindrical shape whose one end is closed, and has, on its closed end, i.e., on its bottom wall 961, a pair of tubular parts in which a pair of insertion openings 963 and 964 are formed for allowing both ends of the arc tube to be inserted therethrough. The holding member 906 holds the arc tube by bonding the ends of the arc tube that have been inserted therein through the insertion openings 963 and 964 to the inner surface of the holding member 906 via a bonding agent.
Although compact self-ballasted fluorescent lamps including the above-described arc tube whose end portions are formed in a double spiral can have a low total height substantially the same as that of incandescent lamps, a problem still remains as that inserting the ends of the arc tube thorough the insertion openings 963 and 964 of the holding member 906 is extremely difficult. To be more specific, the insertion of the ends of the arc tube is extremely difficult because the insertion openings 963 and 964 are provided in directions opposite to each other. Once one end of the arc tube is inserted through the insertion opening 963, the other end of the arc tube goes off from the insertion opening 964.
The insertion of the ends of the arc tube through the insertion openings 963 and 964 can be made relatively easy by enlarging the insertion openings 963 and 964. If the insertion openings 963 and 964 are large, however, another problem arises when the ends of the arc tube are bonded to the inner surface of the holding member 906 via a bonding agent. The problem is that the bonding member may flow out from the insertion openings 963 and 964, thereby leading to serious degradation of the appearance.